Thrombocytopenia in pregnancy

A normal uncomplicated pregnancy is associated with a platelet count in the normal range though up to 10% of normal deliveries may be associ-36 ated with mild thrombocytopenia (>100 x 109/L). Detection of thrombocytopenia in a pregnant patient requires consideration not only of the diagnoses listed in the previous section but also the conditions associated with pregnancy which cause thrombocytopenia. An additional important consideration is the possible effect on the fetus and its delivery.

If thrombocytopenia is detected late in pregnancy, most women will have a platelet count result from the booking visit (at 10-12 weeks) for comparison. Mild thrombocytopenia (100-150 x 109/L) detected for the first time during an uncomplicated pregnancy is not associated with any risk to the fetus nor does it require special obstetric intervention other than hospital delivery.

Non-immune thrombocytopenia

• Thrombocytopenia may develop in association with pregnancy-induced hypertension, pre-eclampsia or eclampsia. Successful treatment of hypertension may be associated with improvement in thrombocytopenia which is believed to be due to consumption. Treatment of hypertension, pre-eclampsia or eclampsia may necessitate delivery of the fetus who is not at risk of thrombocytopenia.

• A number of obstetric complications, notably retention of a dead fetus, abruptio placentae and amniotic fluid embolism, are associated with DIC (M p512).

Immune thrombocytopenia may occur in pregnancy and women with chronic ITP may become pregnant. Therapeutic considerations must include an assessment of the risk to the fetus of transplacental passage of antiplatelet antibody causing fetal thrombocytopenia and a risk of haemorrhage before or during delivery. There is no reliable parameter for the assessment of fetal risk which, although relatively low, is most significant in women with pre-existing chronic ITP. Note: the severity of the mother's ITP has no bearing on the fetal platelet count.

Women with a platelet count <20 x 109/L due to ITP should receive standard prednisolone therapy or IVIg (ffl p388). If prednisolone fails or is contraindicated, IVIg should be administered and may need to be repeated at 3 week intervals. Splenectomy should be avoided (high rate of fetal loss). Enthusiasm has waned for assessing the fetal platelet count during pregnancy by cordocentesis followed by platelet transfusion. Fetal scalp sampling in early labour is unreliable and hazardous. Delivery should occur in an obstetric unit with paediatric support and the neonate's platelet count should be monitored for several days as delayed falls in the platelet count occur.

BCSH Guidelines (2003) Guidelines for the investigation and management of idiopathic thrombocytopenic purpura in adults, children and in pregnancy. Br J Haematol, 120, 574-596.